I understand what you are saying, but the dampner on a 400 is considerably different than on a 350 or any other gen1 sbc. Though they are the same thickness,but the 400 dampner has a slot machined about half the circumference of the dampner. It's my understanding that it is the only style that will work on a stock 400sbc an must be used in conjunction with a flex plate with added weight on the backside or a flywheel from a 454bbc. I only know this because of the problems I had when I dropped a 400sbc in a '62 pickup and hooked a 3 speed behind it.